Look at What the Cat Dragged in: A Never-Before-Seen Exotic Virus

Your feline friend may be bringing home more than you bargained for. Those mousey hunting trophies dropped at your door might contain exotic viruses completely unknown to us, as new research suggests.

In a recent paper, researchers in Florida describe discovering a microbe inside a dead rodent that had been caught by one of the scientists’ pets, a black male cat named Pepper. Thankfully, this unexpected discovery didn’t make Pepper sick, but the virus might still pose a risk to humans.

There are all sorts of viruses and other microbes left uncatalogued in the world. And while most of these pose no danger to us, some may have the machinery and opportunity needed to jump across species and become a real problem—also known as a spillover event. This latest discovery, made by researchers at the University of Florida, illustrates the value of looking for viral threats in less conventional places.

Pepper belongs to John Lednicky, a UF microbiologist and long-time virus hunter who lives in Gainesville, Florida. In early May 2021, Pepper dragged in a fresh rodent kill, a common cotton mouse (Peromyscus gossypinus). While Pepper’s penchant for dropping off furry gifts was nothing new, Lednicky decided to do something different with it this time. He wondered if these mice could possibly carry mule deerpox virus (MDPV), a potentially emerging pathogen in white tailed deer that had recently been found in the state. So, he and his team brought the dead rodent back to the lab to study it further. While the researchers didn’t spot the mule deerpox virus in Pepper’s specimen, they did find something previously never seen in the U.S.: a type of jeilongvirus.

Pepper the cat laying in his owner John Lednick’s lap. © John Lednicky

Jeilongviruses are part of a broad viral family called paramyxoviruses, some of which include germs that make us sick, like those that cause measles and mumps. Other jeilongviruses have been found in Africa, Asia, Europe, and South America. They seem to primarily infect rodents, but some are capable of also infecting other species like bats and cats. And the team’s early research suggests that their virus is unlike any other of its kind seen to date. In the lab, they found that it could infect and grow inside human and other primate cells just as easily as it could inside rodent cells—a worrying sign that it has spillover potential.

The researchers have dubbed their novel microbe the Gainesville rodent jeilong virus 1 (GRJV1). They detailed their findings on GRJV1 in a paper published last month in the journal Pathogens.

“We were not anticipating a virus of this sort, and the discovery reflects the realization that many viruses that we don’t know about circulate in animals that live in close proximity to humans. And indeed, were we to look, many more would be discovered,” said lead author Emily DeRuyter, a doctoral candidate at UF’s Department of Environmental and Global Health, in a statement from the university.

The actual threat that GRJV1 may pose to us right now is likely low. Even if it could infect people outside the lab, we generally aren’t coming into close contact with potential rodent vectors all that often these days. The researchers note that even well-known, deadly rodent-borne germs like hantaviruses only occasionally cause outbreaks in humans.

More research is needed to understand how GRJV1 interacts with its rodent hosts and other potential animals—does it make them sick, for instance? And it’s still important to figure out whether GRJV1 can or has already spilled over to humans in the past. While most spillover events are isolated and lead nowhere, the occasional pathogen can sometimes successfully jump over the species barrier and become a newly established human disease (the virus formerly known as monkeypox is one such recent example). Tracking and looking for these zoonotic viruses can help us prepare against and potentially prevent these events.

For his part, Pepper’s virus hunting seems to have left him no worse for wear.

“Cats, in general, evolved to eat rodents, and are not sickened by the viruses carried by rodents,” said Lednicky in a statement, “but we have to do tests to see whether the virus affects pets, and humans.”